1. Technical Field
The present invention relates to a fan rotation speed controlling device. More particularly, the present invention relates to a fan rotation speed controlling device applicable to, and capable of controlling the rotation speeds of, a plurality of electrically connected fans which are of different specifications.
2. Description of Related Art
A personal computer system is typically installed with a variety of heat dissipation fans to ensure that all the electronic components work at proper temperatures. However, the wind shear generated by the heat dissipation fans during operation turns out to be the major source of noise in a computer. The higher the rotation speeds of the heat dissipation fans, the more noise is generated by the resulting wind shear. Therefore, with a view to noise reduction, it is important to effectively control the rotation speeds of the fans when the system is idle.
Nowadays, the motherboard of a computer controls a heat dissipation fan mainly in two ways, either by voltage control (VC) or by pulse-width modulation (PWM) control.
VC is the earlier developed of the two control approaches and is applicable to 3-pin fans. More specifically, temperature is detected by a temperature sensor on the motherboard, and voltage is adjusted according to the detection result in order to control the rotation speed of a fan and thereby achieve the intended heat dissipation effect. This approach is advantageous in that a voltage controlled fan (or VC fan for short) is relatively low-cost and that the required circuit is relatively simple. However, noise associated with magnetic shear is generated as the operating voltage of a VC fan is repeatedly switched between high and low levels. Moreover, a VC fan responds relatively slow to rotation speed control.
The more recent PWM control approach, on the other hand, is applicable to 4-pin fans. The additional fourth pin serves to receive from the motherboard a PWM signal for controlling the rotation speed of the fan. This explains why a PWM controlled fan (or PWM fan for short) responds to rotation speed control faster and more accurately than a VC fan. However, a PWM fan has a higher production cost attributable to the built-in PWM signal control IC. Furthermore, a PWM fan cannot be used unless the motherboard supports such fans.
As stated above, both VC and PWM control rely on the support of the motherboard. A PWM fan cannot be applied to a motherboard which only provides voltage control; nor can a VC fan be driven by a PWM signal. Consequently, the existing VC fans and PWM fans are limited in use.
The issue to be addressed by the present invention is to solve the aforementioned problems of the prior art.